UM10503
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© NXP B.V. 2012. All rights reserved.
User manual
Rev. 1.3 — 6 July 2012
97 of 1269
NXP Semiconductors
UM10503
Chapter 11: LPC43xx Clock Generation Unit (CGU)
The CGU selects the inputs to the clock generators from multiple clock sources, controls
the clock generation, and routes the outputs of the clock generators through the clock
source bus to the output stages. Each output stage provides an independent clock source
and corresponds to one of the base clocks for the LPC43xx. See
for a
description of each base clock and
for the possible clock sources for each base
clock.
The CGU contains four types of clock generators:
1. External clock inputs and internal clocks: The external clock inputs are the Ethernet
PHY clocks and the general purpose input clock GP_CLKIN. The clocks from the
internal oscillators are the IRC and the 32 kHz oscillator output clocks. These clock
generators have no selectable inputs from the clock source bus and provide one clock
output each to the clock source bus.
2. Crystal oscillator: The crystal oscillator is controlled by the CGU. The input to the
crystal oscillator are the XTAL pins. The crystal oscillator creates one output to the
clock source bus.
3. PLLs: PLL0USB, PLL0AUDIO, and PLL1 are controlled by the CGU. Each PLL can
select one input from the clock source bus and provides one output to the clock
source bus. The input to the PLLs can be selected from all external and internal
clocks and oscillators, from the other PLLs, and from the outputs of any of the integer
dividers (see
). One PLL0 cannot select the other PLL0 as input.
4. Integer dividers: Each of the five integer dividers can select one input from the clock
source bus and creates one divided output clock to the clock source bus. The input to
all integer dividers can be selected from all external and internal clocks and
oscillators, and from all three PLLs. In addition, the output of the first integer divider
can be selected as an input to all other integer dividers (see
).
Fig 25. CGU and CCU1/2 block diagram
32 kHz OSC
PLL0
(AUDIO)
PLL0
(USB0)
IDIVA
/4
IDIVB
/16
IDIVE
/256
OUTCLK1- 6, 9 - 10
(BASE_xxx_CLK)
OUTCLK12 - 19
(BASE_xxx_CLK)
CRYSTAL OSC
PLL1
IDIVC
/16
IDIVD
/16
BASE_SAFE_CLK
OUTCLK20
OUTCLK7
OUTCLK8
OUTCLK11
12 MHz IRC
ENET_RX_CLK
LCD_CLK
ENET_TX_CLK
GP_CLKIN
8
8
CGU
XTAL1
RTCX1
RTCX2
XTAL2
CCU1
CCU2
branch clocks to core
and peripherals
branch clocks to
peripherals
CLKOUT
OUTCLK25
APLL
OUTCLK26
CGU_OUT0
OUTCLK27
CGU_OUT1
WWDT
ETHERNET